The kit contains stories from celebrities including Pamela Anderson and Bill Clinton, five easy steps to transition to a vegetarian diet, a Meet Your Meat section detailing what happens to animals prior to consumption and a range of vegan recipes.

Campaign coordinator Claire Fryer told ABC Radio on October 11: "Those who do follow a plant-based diet are several kilos lighter on average than those who do eat meat. Australia now is one of the fattest nations, and it's not just simply the risk of obesity that's reduced but children and adults who go vegan can reduce their risk of cancer, heart disease, diabetes, strokes and numerous very serious conditions."

It's well known that Australia is one of the fattest developed nations.The federal Health Department says 18 per cent of males and 17 per cent of females were obese in 2004-05, while 20 to 25 per cent of children were overweight or obese in 1995.

But can a vegetarian/vegan diet really combat obesity and reduce the risk of disease?

The claim: Animal rights group PETA says vegetarians and vegans weigh less than meat eaters and have a reduced risk of diseases such as cancer, heart disease, diabetes and strokes.

The verdict: PETA's claim is correct, but there's more to the story. A poorly planned vegetarian/vegan diet can result in nutritional deficiencies and other health problems, and it is misleading to suggest an absence of meat alone will bring about weight loss.

The article summarises the findings of a scientific review titled 'Vegetarian Diets and Weight Status', published in the journal Nutrition Reviews in 2006. "Vegetarian diets are associated with reduced body weight, lower incidence of certain chronic disease, and lower medical costs compared with non-vegetarian diets," it says.

The Physicians Committee for Responsible Medicine is made up of physicians, healthcare professionals, veterinarians, and "compassionate laypersons". It advocates for "ethical research" and to "end cruelty to animals". It promotes a vegan diet and the consumption of four food groups - fruit, legumes, whole grains and vegetables.

Nutrition Reviews is an international, not-for-profit journal which seeks "to further the understanding of scientific issues relating to nutrition, food safety... and the environment by bringing together scientists from academia, government, and industry".

Read the research:

A 2013 study of 44,000 men and women living in England and Scotland, of whom 34 per cent consumed a vegetarian diet, found "compared with non-vegetarians, vegetarians had a lower mean BMI [body mass index]".

A 2012 study assessed the effect of a low-fat, vegan diet in 64 overweight, postmenopausal women. "A vegan diet was associated with significantly greater weight loss than the NCEP diet at 1 and 2 years," it found.

A 2009 study surveyed more than 2,500 Americans aged 15 to 23. It found "vegetarians were less likely than never vegetarians to be overweight or obese." However it noted adolescent and young adult vegetarians may be at increased risk of eating disorders.

A 2008 study analysed 215 Australian teenagers from Adventist schools. "Adolescents consuming predominantly vegetarian foods showed significantly better scores on markers of cardiovascular health, including, BMI, waist circumference, cholesterol/high density lipoprotein ratio and low density lipoprotein," it found. However, the study noted that because Adventists are experienced vegetarians, "the health benefits attributed to this vegetarian cohort may not be seen in children with significantly different vegetarian diet patterns".

A 2006 study investigated changes in weight and BMI over a five-year period in meat-eating, fish-eating, vegetarian, and vegan men and women in the United Kingdom. It found weight gain was somewhat smaller in vegans and fish-eaters compared with meat-eaters. "Lowest weight gain was seen among those who, during follow-up, had changed to a diet containing fewer animal food," it said.

A 2006 study of vegetarian women in Australia found vegetarians and semi-vegetarians had lower BMI than non-vegetarians. However, it also found semi-vegetarians and vegetarians had poorer mental health and more menstrual problems.

A 2002 study compared BMI in 38,000 people in the UK across four diet groups. It found "fish-eaters, vegetarians and especially vegans had lower BMI than meat-eaters" and that "high protein and low fibre intakes were the factors most strongly associated with increasing BMI".

Risk of disease

The federal Health Department says a number of diseases are associated with obesity.

Fact Check asked Ms Fryer for the basis of her claim that "children and adults who go vegan can reduce their risk of cancer, heart disease, diabetes, strokes and numerous very serious conditions". She referred to a 2003 publication by the American Dietetic Association and Dietitians of Canada.

It found "planned vegetarian diets are healthful, nutritionally adequate, and provide health benefits in the prevention and treatment of certain disease". Vegetarians show "lower blood cholesterol levels; lower blood pressure; and lower rates of hypertension, type 2 diabetes, and prostate and colon cancer", it said.

A 2005 study titled Vegetarian Diets: What are the Advantages reiterated those findings. "In most cases, vegetarian diets are beneficial in the prevention and treatment of certain diseases, such as cardiovascular disease, hypertension, diabetes, cancer, osteoporosis, renal disease and dementia, as well as diverticular disease, gallstones and rheumatoid arthritis," it said.

And a 2013 study of 44,561 men and women living in England and Scotland - 34 per cent of whom were vegetarian - found "consuming a vegetarian diet was associated with lower IHD [ischemic heart disease] risk".

What the experts say

The president of the Australian Medical Association, Dr Steve Hambleton, says while there is some substance to PETA's claims, advocating "a vegan or vegetarian diet for all is an extreme view".

"If you're a vegan and you don't eat sardines you're missing out on your Omega 3," he said. "So extremes of any diet are not going to be healthy."

Dr Hambleton says it is true that obesity increases the risk of certain diseases, and that some Australians may need to cut back on their meat intake. "Meat is a good source of iron and clearly we are omnivores so we are designed to eat meat, but not only meat," he said.

Surinder Baines, an Associate Professor from the University of Newcastle's School of Health Sciences, says most studies have confirmed that vegetarians and vegans have lower BMIs than people who eat meat.

Associate Professor Baines says the lower BMIs are partly explained by their diet, but that vegetarians also tend to have higher physical activity, limit their alcohol intake and avoid smoking. "So you have to take into account their other lifestyle factors," she said.

She says lower BMIs may in part explain their reduced risk of some chronic disease, "such as diabetes, hypertension, heart disease and some forms of cancer".

Dr Neil Mann, a professor of food science and nutrition from RMIT University, says while PETA's claims are technically true, they mislead the public. He says the main reason vegetarians and vegans weigh less than meat eaters and have reduced risk of disease is because they have low intakes of "high fat, sugar, starch, processed and take away foods".

Dr Mann says there are also studies which show that eating lean meat can reduce weight. "You can eat meat and lose weight, it just depends on what you're eating with it," he said.

Aloysa Hourigan is a senior nutritionist from Nutrition Australia, an independent, not-for-profit organisation. Ms Hourigan says it is important to note that vegetarians can have nutritional deficiencies including iron, zinc and B12.

However, experts say a carefully planned diet can ensure those nutritional needs are met. The Australian Dietary Guidelines offer the following advice:

"Appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthy and nutritionally adequate. Well-planned vegetarian diets are appropriate for individuals during all stages of the lifecycle. Those following a strict vegetarian or vegan diet can meet nutrient requirements as long as energy needs are met and an appropriate variety of plant foods are eaten throughout the day. Those following a vegan diet should choose foods to ensure adequate intake of iron and zinc and to optimise the absorption and bioavailability of iron, zinc and calcium. Supplementation of vitamin B12 may be required for people with strict vegan dietary patterns."

The World Health Organisation says obesity is largely preventable, but it does not advocate giving up meat as a solution. It says at the individual level, people can:

Limit energy intake from total fats and sugars;

Increase consumption of fruit and vegetables, as well as legumes, whole grains and nuts;

Engage in regular physical activity.

The starter kits distributed by PETA acknowledge the need for vegetarians and vegans to ensure they include protein, iron and vitamin B12 in their diets.

The verdict

Ms Fryer is correct to say that vegans and vegetarians on average weigh less than those who eat meat. She is also correct to say people on a vegan/vegetarian diet can reduce their risk of illnesses such as cancer, heart disease, diabetes and strokes.

However, a poorly planned vegetarian/vegan diet can result in nutritional deficiencies and other health problems, and it is misleading to suggest an absence of meat alone will bring about weight loss. Obesity is a complex issue caused by a variety of factors.

It's a fundamental human yearning to be a part of something bigger than one's self, and maybe that's what drove my mate Ash to die, far from home, in a bloody foreign war against Islamic State, writes C August Elliott.